Trying to reduce memory footprint of json reads
Heavy filtering to eliminate any non-desired KA translations.
Merge commit 'dbaaf5fa4e4b909a489008ce69c97c9c00b7486b' from Ben into 1293

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
fix some merge bugs to make update_language_packs work again
add new --low-mem option
convert use of filter into itertools.filter
convert prep_inputs back into generator